1. Field of the Invention
The present invention relates to a method of manufacturing hot rolled steel strip from continuously cast input stock in successive work steps, wherein, after solidification, strip-shaped input stock is adjusted to hot rolling temperature and the input stock is introduced into a multiple-stand rolling mill for rolling into finished strip.
2. Description of the Related Art
In accordance with a newly developed technology for the economical manufacture of hot wide strip, a so-called thin slab having a thickness of, for example, 50 mm, is produced in a continuous casting machine particularly constructed for this purpose. After solidification and temperature equalization, the thin slabs are conveyed in a roller conveyor furnace to the rolling train and are rolled to the desired final thickness.
When designing the rolling plant, it is important for economical reasons to use as few roll stands as possible. Rolling plants have already been realized which make it possible, with strip widths of up to 1350 mm for steels having low carbon contents, to achieve a final thickness of 2.5 mm by using only four roll stands. Such a plant is already known from DE 36 37 893 A1. In the known method and the arrangement for carrying out the method, the strip-shaped input stock is adjusted to rolling temperature after solidification and is introduced into a rolling mill for rolling out into finished strip, wherein rolling is carried out continuously in at most three or four roll stands with the pass reductions being as great as possible. In the first two roll stands, approximately maximum rolling moments and large work roll diameters are used.
However, more stands are required when smaller final thicknesses and greater widths of the rolled stock are to be obtained. Consequently, because of the greater length of the plant resulting from the increased temperature drop, an increase of the rolling speed must be accepted. However, because of the increased drive powers required for this purpose, this increase of the rolling speed is frequently not desirable and not even feasible. In addition, usually not more than seven stands are considered for a rolling train.
However, for example, in the case of increased material strengths, it may even be possible that a train with seven stands is not capable of achieving final thicknesses of less than 2 mm if the steel strip has a great width. The reason for this limitation of the reduction capacity is essentially the fact that the permissible reduction must be limited in the first stand because of the cast structure present in the first stand. This is a particular disadvantage because in the first stand the rolling temperature still is in the order of magnitude of 1,000.degree. C., so that great reductions would be possible because of the low material strength. In the second stand, on the other hand, the material has already essentially recrystallized and the temperature of the rolled stock has dropped by approximately 50.degree. C. Consequently, the possible pass reduction in the second stand is limited by the required rolling moment or the required rolling force. Even if the maximum stand capacity is utilized in the second stand and all following stands, the desired final thickness of less than 2 mm can frequently not be achieved.